In general, a domain name represents an IP address and is associated to it in the Domain Name System (DNS). This article explains how to configure domain name resolution and resolve domain names. Show
Name Service SwitchThis article or section needs expansion.The Name Service Switch (NSS) facility is part of the GNU C Library (glibc) and backs the getaddrinfo(3) API, used to resolve domain names. NSS allows system databases to be provided by separate services, whose search order can be configured by the administrator in nsswitch.conf(5). The database responsible for domain name resolution is the hosts database, for which glibc offers the following services:
systemd provides three NSS services for hostname resolution:
Resolve a domain name using NSSNSS databases can be queried with getent(1). A domain name can be resolved through NSS using: $ getent hosts domain_name Glibc resolverThe glibc resolver reads resolv.conf(5) lists nameservers together with some configuration options. Nameservers listed first are tried first, up to three nameservers may be listed. Lines starting with a number sign ( Note: The glibc resolver does not cache queries. To improve query lookup time you can set up a caching resolver. Glibc resolver also can not validate DNSSEC. A DNSSEC capable validator resolver is required for that one. See #DNS servers for more information. Overwriting of /etc/resolv.confNetwork managers tend to overwrite
To prevent programs from overwriting # chattr +i /etc/resolv.conf Tip: If you want multiple processes to write to Limit lookup timeIf you are confronted with a very long hostname lookup (may it be
in pacman or while browsing), it often helps to define a small timeout after which an alternative nameserver is used. To do so, put the following in options timeout:1 Hostname lookup delayed with IPv6If you experience a 5 second delay when resolving hostnames it might be due to a DNS-server/Firewall misbehaving and only giving one reply to a
parallel A and AAAA request.[1] You can fix that by setting the following option in options single-request Local domain namesTo be able to use the hostname of local machine names without the fully qualified domain name, add a line to domain example.org That way you can refer to local hosts such as Lookup utilitiesTo query specific DNS servers and DNS/DNSSEC records you can use dedicated DNS lookup utilities. These tools implement DNS themselves and do not use NSS. ldns provides drill(1), which is a tool designed to retrieve information out of the DNS. For example, to query a specific nameserver with drill for the TXT records of a domain: $ drill @nameserver TXT domain Unless a DNS server is specified, drill will use the nameservers defined in Resolver performanceThe Glibc resolver does not cache queries. To implement local caching, use systemd-resolved or set up a local caching
DNS server and use it as the name server by setting Tip:
Privacy and securityThe DNS protocol is unencrypted and does not account for confidentiality, integrity or authentication, so if you use an untrusted network or a malicious ISP, your DNS queries can be eavesdropped and the responses manipulated. Furthermore, DNS servers can conduct DNS hijacking. You need to trust your DNS server to treat your queries confidentially. DNS servers are provided by ISPs and third-parties. Alternatively you can run your own recursive name server, which however takes more effort. If you use a DHCP client in untrusted networks, be sure to set static name servers to avoid using and being subject to arbitrary DNS servers. To secure your communication with a remote DNS server you can use an encrypted protocol, like DNS over TLS (RFC 7858), DNS over HTTPS (RFC 8484), or DNSCrypt, provided that both the upstream server and your resolver support the protocol. An alternative can be a dedicated software to encrypt and decrypt the communication, such as stunnel. To verify that responses are actually from authoritative name servers, you can validate DNSSEC, provided that both the upstream server(s) and your resolver support it. Application-level DNSBe aware that some client software, such as major web browsers[2][3], are starting to implement DNS over HTTPS. While the encryption of queries may often be seen as a bonus, it also means the software sidetracks queries around the system resolver configuration.[4] Firefox provides configuration options to enable or disable DNS over HTTPS and select a DNS server. Chromium will examine the user's system resolver and enable DNS over HTTPS if the system resolver addresses are known to also provide DNS over HTTPS. See this blog post for more information and how DNS over HTTPS can be disabled. Mozilla
has proposed universally disabling application-level DNS if the system resolver cannot resolve the domain Oblivious DNSOblivious DNS is a system which addresses a number of DNS privacy concerns. See Cloudflare's article for more information. Third-party DNS servicesNote: Before using a third-party DNS service, check its privacy policy for information on how user data is handled. User data has value and can be sold to other parties. There are various third-party DNS services available, some of which also have dedicated software:
You can use dnsperftest to test the performance of the most popular DNS resolvers from your location. dnsperf.com provides global benchmarks between providers. DNS serversDNS servers can be authoritative and recursive. If they are neither, they are called stub resolvers and simply forward all queries to another recursive name server. Stub resolvers are typically used to introduce DNS caching on the local host or network. Note that the same can also be achieved with a fully-fledged name server. This section compares the available DNS servers, for a more detailed comparison, refer to Wikipedia:Comparison of DNS server software. This article or section needs expansion.
Conditional forwardingIt is possible to use specific DNS resolvers when querying specific domain names. This is particularly useful when connecting to a VPN, so that queries to the VPN network are resolved by the VPN's DNS, while queries to the internet will still be resolved by your standard DNS resolver. It can also be used on local networks. To implement it, you need to use a local resolver because glibc does not support it. In a dynamic environment (laptops and to some extents desktops), you need to configure your resolver based on the network(s) you are connected to. The best way to do that is to use openresolv because it supports multiple subscribers. Some network managers support it, either through openresolv, or by configuring the resolver directly. NetworkManager supports conditional forwarding without openresolv. Note: Although you could use other conditions for forwarding (for example, source IP address), "conditional forwarding" appears to be the name used for the "domain queried" condition. See also
Which of the following ports would be used to resolve a domain name to an IP?Port 53 (UDP) This port is used to access DNS servers. It must be open to your DNS server IP addresses so that the client can resolve public domain names.
Which of the following commands are used to display or modify the IP address of a network interface?The ipconfig command displays the basic IP addressing information for each network interface on the Windows system. This information includes both the IP address and subnet mask.
What command will show you the DNS server your host is using to resolve hostnames?Use NSLOOKUP to query the DNS server. Note: Skip this step if you found a host name entry in the PC's hosts file, and proceed to step 2. (The hosts file takes precedence over DNS servers when the operating system resolves host names for the PC.) At a command prompt, type NSLOOKUP and press Enter.
Which command must be used on a Linux device to determine the IP configuration of the eth0 network interface?View Network Settings of Specific Interface
Using interface name (eth0) as an argument with the “ifconfig” command will display details of the specific network interface.
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